A risk-benefit assessment of tamoxifen therapy.

Tamoxifen is the endocrine treatment of choice for all women with hormonally responsive breast cancer. 30 years of experience in both the laboratory and clinical setting have shown tamoxifen to be an effective adjuvant treatment with minor short term adverse effects. However, as therapeutic use has extended to 5 years and beyond, and as clinical trials begin which will assess the effectiveness of tamoxifen as a preventive treatment, concern about possible long term adverse effects is justified. Tamoxifen has an estrogen-like influence on the skeletal and cardiovascular systems, resulting in decreases in both postmenopausal bone loss and low density lipoprotein (LDL) levels. These effects will, it is hoped, result in decreases in the incidences of osteoporosis and coronary heart disease, which are major causes of morbidity and mortality in the postmenopausal age group. Tamoxifen therapy also results in decreased rates of contralateral breast cancer. Long term tamoxifen treatment may result in a small increase in the incidence of endometrial and/or hepatocellular carcinoma, but with millions of women taking tamoxifen for long periods, such small increases in incidence translate to a significant number of women at risk. Tamoxifen is clearly beneficial for short term treatment, but the clinical decision of tamoxifen use in the long term must be made on the individual benefits versus risks of tamoxifen treatment.